Off-center angle measurement system

ABSTRACT

A method for measuring an angular position of a rotating shaft, the method including providing a magnetic field which rotates with the shaft about an axis of rotation, positioning an integrated circuit having first and second magnetic sensing bridges within the magnetic field at a radially off-center position from the axis of rotation, the first and second magnetic sensing bridges respectively providing first and second signals representative of first and second magnetic field directions, the integrated circuit having a set of adjustment parameters for modifying attributes of the first and second signals, modifying values of the set of adjustment parameters until errors in the first and second signals are substantially minimized, and determining an angular position of the shaft based on the first and second signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of patent application Ser. No. 14/286,607, filed on May 23, 2014, now U.S. Pat. No. 9,606,194, which is a continuation-in-part of patent application Ser. No. 13/267,534, filed on Oct. 6, 2011, now U.S. Pat. No. 8,736,257, which is a continuation of patent application Ser. No. 12/206,410, filed Sep. 8, 2008, now U.S. Pat. No. 8,058,866, all of which are incorporated herein by reference.

BACKGROUND

Magnetic sensing devices, such as Giant Magnetoresistance (GMR) sensors, for example, are used in a wide variety of applications. For example, GMR sensors are often used for sensing the angular position of a rotating member, such as a motor shaft. In such applications, a permanent magnet, sometimes referred to as a “pill”, is typically mounted to or embedded in an end of the motor shaft and is centered on the axis of rotation. The GMR elements or resistors, which are typically connected to form one or more bridges, are also positioned so as to be centered on the axis of rotation, with the resulting output signals generated by the GMR resistors being indicative of the angular position of the rotating shaft.

However, for many reasons, such as space limitations, for example, it may not always be possible or desirable to position an angle sensor, such as a GMR sensor at the end of the rotating shaft. In such instances, toothwheels or polewheels are sometimes mounted to the rotating shaft and a magnetic sensor (e.g. a Hall effect sensor) are positioned proximate to the wheel and detect the passing of each tooth or pole to determine the angular position of the rotating shaft. However, while toothwheels and pole wheels are typically very accurate, they can be quite costly and provide only discrete (not continuous) location measurements as compared to magnetoresistive-based angle sensors, such as GMR type angle sensors, for example.

For these and other reasons, there is a need for the embodiments of the present disclosure.

SUMMARY

One embodiment provides a method for measuring an angular position of a rotating shaft. The method includes providing a magnetic field which rotates with the shaft about an axis of rotation, positioning an integrated circuit having first and second magnetic sensing bridges within the magnetic field at a radially off-center position from the axis of rotation, the first and second magnetic sensing bridges respectively providing first and second signals representative of first and second magnetic field directions, the integrated circuit having a set of adjustment parameters for modifying attributes of the first and second signals, modifying values of the set of adjustment parameters until errors in the first and second signals are substantially minimized, and determining an angular position of the shaft based on the first and second signals.

Another embodiment provides an integrated circuit for measuring an angular position of a magnetic object rotating around an axis from an off-axis position. The integrated circuit may include a plurality of magnetic sensing elements and a plurality of switches. The plurality of switches may be configured to select a first subset of one or more sensing elements out of the plurality of magnetic sensing elements. The subset of sensing elements may provide a first signal representative of a first directional component of a magnetic field caused by the rotating magnetic object.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

FIG. 1 is an end view of an off-center angle measurement system according to one embodiment.

FIG. 2 is a side view of the off-center angle measurement system of FIG. 1.

FIG. 3 a block diagram generally illustrating one embodiment of a GMR angle sensor suitable for use with the off-center angle measurement system of FIG. 1.

FIG. 4 is a schematic diagram generally illustrating a GMR resistor configuration according to one embodiment.

FIG. 5 is a graph illustrating examples of output curves provided by the GMR angle sensor of FIG. 3.

FIG. 6 is a diagram illustrating an example of a GMR sensor positioned at a center of rotation of a magnet according to one embodiment.

FIG. 7 is a graph of angle error from non-uniform magnetic field.

FIG. 8 is a graph of simulated error caused by adjusting amplitude parameters.

FIG. 9 is a graph of simulated error caused by adjusting orthogonality parameter.

FIG. 10 is graph of error caused by radial position relative to magnet.

FIG. 11 is schematic diagram of an array of GMR resistors according to one embodiment.

FIGS. 12A through 12C illustrate examples of GMR sensor bridge configurations according to one embodiment.

FIG. 13 is a flow diagram illustrating an operating and calibration procedure according to one embodiment.

FIG. 14 illustrates one example of an integrated circuit according to one embodiment.

FIG. 15 illustrates one example of an integrated circuit according to another embodiment.

FIG. 16 illustrates one example of integrated circuits according to another embodiment.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

FIGS. 1 and 2 respectively illustrate end and side views of an off-center GMR angle-measurement system 30 according to one embodiment which, as will be described in greater detail below, employs a plurality of adjustable GMR parameters to correct angle measurement errors caused by non-linear magnetic field lines.

It is to be understood that GMR type sensors are mentioned within this disclosure as a mere example of magnetic sensors, in particular angle sensors. Therefore the terms GMR sensor, GMR angle sensor and the like shall be construed as representing any known type of magnetic sensor or angle sensor, including but not limited to TMR sensors, AMR sensors, Hall sensors, vertical Hall sensors, horizontal Hall sensors. Likewise terms such as GMR resistor region, GMR sensor bridge, GMR amplitude parameter, GMR angle measurement system, or GMR parameter shall be construed as representing the corresponding resistor region, sensor bridge, amplitude parameter, angle measurement system, or parameters in any known type of magnetic sensor, or any known type of angle sensor.

According to one embodiment, off-center angle measuring system 30 includes a permanent ring magnet 32, divided equally into a north pole 34 (indicated by the “filled” area) and a south pole 36 (indicated by the “shaded” area), mounted on a rotating member 38, such as a rotating motor shaft, and a GMR angle sensor 40. A magnetic field of ring magnet 32 extends from north pole 34 to south pole 36, as indicated by magnetic field lines 42 a through 42 d.

A person of ordinary skill in the art will readily appreciate that more than one pair of north pole and south pole may be arranged along a circumferential direction of the permanent ring magnet 32. Such an arrangement would however lead to more than one period of sinus or cosine signals for a full rotation of the permanent magnet 32 providing a higher angular solution with regards to a change in angular position. As a tradeoff one would lose the option to distinguish an absolute angular position over a full turn of the rotating object. Which may however not be required in some applications.

According to one embodiment, GMR angle sensor 40 comprises a semiconductor chip having a GMR resistor region 44 (i.e. a “sensitive” region) mounted on a printed circuit board (PCB) 46. According to one embodiment, PCB 46 and thus, GMR angle sensor 40, are positioned in a plane 47 parallel to a surface 48 of ring magnet 32 such that resistor region 44 is substantially centered along an x-axis 50 extending through an axis of rotation 52 of rotating shaft 38 and between an inner radius (Ri) 54 and an outer radius (Ro) 56 of ring magnet 32. For purposes of the description herein, a 0-degree angular position of rotating shaft 38 is defined as being along x-axis 50, as indicated at 58, a 90-degree position is defined as being along y-axis 60 (perpendicular to and extending through axis of rotation 52), as indicated at 62, and so on. A direction of rotation of rotating shaft 38 is by rotational arrow 64.

FIG. 3 is a block diagram generally illustrating one embodiment of GMR angle sensor 40 when configured as a semiconductor chip. As illustrated, in addition to GMR resistor region 44, GMR angle sensor 40 further includes a controller 70 and a memory 72, with memory 72 storing values for a plurality of GMR parameters 74, which will be described in greater detail below. GMR angle sensor 40 further includes a plurality of PINs, such as a supply voltage (V_(DD)) pin 76, a ground pin 78, and a data I/O pint 80.

FIG. 4 is a schematic diagram generally illustrating GMR resistor region 44 according to one embodiment. As illustrated, GMR resistor region 44 includes a pair of GMR sensor bridges 90 and 92, with sensor bridge 90 formed by four GMR resistors 94 a-94 d and sensor bridge 92 formed by four GMR resistors 96 a-96 d. According to the bridge implementation of FIG. 4, GMR sensor bridges 90 and 92 are disposed orthogonal to one another and are respectively configured to sense an x-component and a y-component of a rotating magnetic field, such as the magnetic field indicated by the dashed lines at 98.

A supply voltage V_(DD) 100 is applied to a terminal 102 via pin 76 and voltage signals V_(X)+ and V_(X)− of GRM sensor bridge 90 are measured at terminals 104 and 106, and voltage signals V_(Y)+ and V_(Y)− of GMR sensor bridge 92 are measured at terminals 108 and 110. In response to an external magnetic field, such as magnetic field 98, one or more of the GMR resistors 94 a-94 d and 96 a-96 d change in their electrical resistances, causing changes in voltage signals V_(X)+ and V_(X)− at terminals 104 and 106 and voltage signals V_(Y)+ and V_(Y)− at terminals 108 and 110 which are representative of an angular position of magnetic field 98 relative to a reference vector (e.g. 0-degrees).

FIG. 5 is a graph 120 illustrating an “ideal” output signals V_(X)(COS) 122 and V_(Y)(SIN) 124 provided by GMR angle sensor 40 based respectively on voltage signals V_(X)+ and V_(X)− and voltage signals V_(Y)+ and V_(Y)− as magnetic field 98 rotates from 0-360 degrees, as indicated by the angle α at 128. As illustrated by the graph at 130, output signals V_(X)(COS) 122 and V_(Y)(SIN) 124 respectively represent x- and y-components of a vector 132 indicative of the angular position of magnetic field 98. According to one embodiment, output signals V_(X)(COS) 122 and V_(Y)(SIN) 124 are provided to an external device which determines the angular position of magnetic field 98 based on the above relationship.

As mentioned above, graph 120 represents output signals V_(X)(COS) 122 and V_(Y)(SIN) 124 under ideal conditions. Under such ideal conditions, each of the GMR resistors 94 a-94 d and 96 a-96 d are identical, and GMR sensor bridges 90 and 92 are perfectly orthogonal to one another, for example, and output signals V_(X)(COS) 122 and V_(Y)(SIN) 124 provide an exact representation of the angular position of magnetic field 98. However, in reality, due to manufacturing tolerances, there are typically inherent variations between each of the GMR resistors 94 a-94 d and 96 a-96 d which can lead to amplitude and offset variation between output signals V_(X)(COS) 122 and V_(Y)(SIN) 124. Additionally, the directions of fixed magnetic field portions of GMR resistors 94 a-94 d and 96 a-96 d are not likely to be perfectly orthogonal to one another which can phase errors between output signals V_(X)(COS) 122 and V_(Y)(SIN) 124. These amplitude, offset, and phase error, in-turn, lead to errors in the determined angular position of the magnetic field, such as magnetic field 98.

According to one embodiment, GMR sensor 40 includes a plurality of GMR parameters which are employed, such as by controller 70 (see FIG. 3), to adjust and correct output signals V_(X)(COS) 122 and V_(Y)(SIN) 124 to compensate for such variations. According to one embodiment, such GMR parameters are dynamically adjustable, such as via an input pin of GMR sensor 40, and values of GMR parameters 74 are stored in memory 72. Such GMR parameters include adjustable amplitude and offset parameters for each of the output signals V_(X)(COS) 122 and V_(Y)(SIN) 124, and an orthogonality parameter to adjust the phase of either V_(X)(COS) 122 or V_(Y)(SIN) 124. The amplitude and offset parameters are employed to substantially equalize the amplitudes of V_(X)(COS) 122 and V_(Y)(SIN) 124, and the orthogonality parameter is adjusted to as to maintain a substantially 90-degree phase shift between V_(X)(COS) 122 and V_(Y)(SIN) 124.

With reference to FIG. 1, one difficulty associated with positioning GMR angle sensor 40 off-center from permanent ring magnet 32 is that magnetic field lines at the perimeter of the magnet are bent or curved. In contrast, as illustrated by FIG. 6, when the GMR resistor region 44 of GMR sensor 40 is centered on an axis of rotation of a permanent magnet, such as that of an example pill-type permanent magnet 132 embedded in an end of a rotating shaft, such as rotating shaft 38, the magnetic field lines passing through GMR resistor region 44 are substantially linear and uniform. However, as illustrated by FIG. 1, when GMR resistor region 44 of GMR sensor 40 is positioned off-center from the axis of rotation of a permanent magnet, such as illustrated by FIG. 1, the magnetic field lines passing through GMR resistor region 44, such as magnetic field line 42 a, are curved and not uniformly spaced. This non-uniformity of the magnetic field can cause errors in output signals V_(X)(COS) 122 and V_(Y)(SIN) 124 generated by GMR angle sensor 40 which, in-turn, cause errors in the measured angle of the rotating shaft to which the permanent magnet is attached, such as rotating shaft 38 to which permanent ring magnet 32 is coupled.

FIG. 7 is a graph 140 illustrating an example of an angle error in the angular position of rotating shaft 38 measured by GMR angle sensor 40 of FIG. 1 and caused by the non-uniformity of the magnetic field at the perimeter of permanent ring magnet 32. As apparent from graph 140, the resulting angle error of curve is approximately sinusoidal in shape over a 360-degree rotation of the rotating shaft. It is noted, however, that errors in the measured angular position of rotating shaft 38 by GMR angle sensor 40 due to inherent amplitude and orthogonality variations between GMR sensor bridges, such as GMR sensor bridges 90 and 92 (and due to variations in the physical construction of GMR angle sensor 40) are also sinusoidal in nature.

For example, FIG. 8 is a graph 150 of a simulated error resulting from an amplitude difference between output signals V_(X)(COS) 122 and V_(Y)(SIN) 124. The simulation was performed by setting the GMR amplitude parameters to values which create a 1% difference in amplitude between V_(X)(COS) 122 and V_(Y)(SIN) 124 with no offset or orthogonality variations. As illustrated by graph 150, the resulting error in the angle measured by GMR angle sensor 40 is sinusoidal in nature over a 360-degree rotation of the magnetic field, with a 1% amplitude resulting in an error varying between 0 and 0.3%.

Similarly, FIG. 9 is a graph 160 of a simulated error resulting from a phase error between output signals V_(X)(COS) 122 and V_(Y)(SIN) 124. The simulation was performed by setting the orthogonality parameter to a value which creates a 0.5-degree variation from a 90-degree phase difference between V_(X)(COS) 122 and V_(Y)(SIN) 124 with no amplitude or offset variations. Again, as illustrated by graph 160, the resulting error in the angle measured by GMR angle sensor 140 is sinusoidal in nature over a 360-degree rotation of the magnetic field, with a 0.5-degree orthogonality error resulting in an error varying between 0 and 0.5%.

According to one embodiment, based on the similar sinusoidal nature of the error in the angle measured by GMR angle sensor 40 resulting from the physical variations between the GMR resistors and GMR sensor bridges and from the non-uniformity of the magnetic field, during a calibration procedure, the GMR parameters of a GMR angle sensor of an off-center GMR angle measuring system, such as GMR angle sensor 40 of off-center GMR angle measuring system 30 of FIG. 1, are adjusted to compensate for errors resulting from the non-uniformity of the off-center magnetic field as well as for error due to amplitude and orthogonality variations.

According to one embodiment, during such a calibration procedure of an off-center angle measurement system, such as off-center GMR angle-measurement system 30 of FIG. 1, rotating shaft 38 is driven so that the angular position of rotating shaft 38 is at a known or actual position during rotation, such as through use of a toothwheel or polewheel based angle measurement system which is temporarily coupled to rotating shaft 38. The angular position of rotating shaft 38 as measured by GMR angle sensor 40 is then compared to the actual position and the values of GMR parameters 74 are adjusted until an error between the angular position of rotating shaft 38 as measured by GMR angle sensor 40 and the actual position is substantially minimized. Again, by adjusting the GMR parameters of GMR angle sensor 40 in this fashion, errors in the angular position as measured by GMR angle sensor 40 resulting from both physical variations of the GMR resistors and GMR sensor bridges and from variations due the non-uniformity of the off-center magnetic field are substantially corrected.

Due to the off-center variations in the magnetic field of the magnet, such as ring magnet 32, the accuracy of the angular position of rotating shaft 38 as measured by GMR angle sensor 40 is also influenced by the position of GMR angle sensor 40 between inner radius 56 and outer radius 58 of permanent ring magnet 32. FIG. 10 is a graph illustrating examples of the magnitude of output vector 142 resulting from GMR angle sensor 40 output signals Vx(COS) 122 and Vy(SIN) 124 when disposed at different positions along x-axis 50 between inner radius 56 and outer radius 58 as shaft 38 rotates over a range of 90-degrees (i.e. 0-90 degrees). In the illustrated example of FIG. 10, ring magnet 32 has an inner radius 56 of 3 mm, and outer radius of 8 mm, and a thickness of 3 mm, with GMR angle sensor 40 being positioned 1.5 mm from surface 48.

Curves 172, 174, 176, 178, 180, 182, and 184 respectively illustrate the magnitude of output vector 142 when GMR angle sensor 40 is positioned at radii of 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, and 10 mm from a center of ring magnet 32. As illustrated by the curves of graph 170, the magnitude of output vector 142 varies as ring magnet 32 rotates with shaft 38, which can cause errors in the angle measurement provided by GMR angle sensor 40. The errors in the angle measurement provided by GMR angle sensor 40 can be reduced by positioning GMR angle sensor at the radial location which results in the least variation in the magnitude of output vector 142. In the example illustrated by FIG. 10, a radial position of 7 mm from a center of ring magnet 32 provides the least amount of variation in magnitude of output vector 142 and represents the best radial location at which to position GRM angle sensor 40.

In view of the above, according to one embodiment, during a calibration procedure of an off-center angle measurement system, such as off-center GMR angle-measurement system 30 of FIG. 1, a radial position of GMR angle sensor 40 relative to ring magnet 32 is adjusted to determine the location which provides the least amount of variation in output vector 142. Such a position corresponds to the position between inner radius 54 and outer radius 56 at which the magnetic field of ring magnet 32 is most uniform.

As illustrated by FIG. 11, according to one embodiment, GMR resistor region 44 includes a first plurality of GMR resistors 190, including GMR resistors 194 a-194 h, having fixed magnetic field portions fixed along an x-axis 192, for example (as indicated by the horizontal arrows in FIG. 11), and a second plurality of GMR resistors 192, including GMR resistors 196 a-196 h, having fixed magnetic field portions fixed along a y-axis 193, for example (as indicated by the vertical arrows in FIG. 11). The first plurality of GMR resistors 190 can be selectively interconnected by an associated plurality of externally controllable switches, as illustrated by switch 200, and the second plurality of GMR resistors 192 can be selectively interconnected by an associated plurality of externally controllable switches, as illustrated by switch 202, to form different GMR sensor bridge configurations (e.g. GMR sensor bridges 90 and 92 of FIG. 4) at different positions along x-axis 191.

For example, as illustrated by FIG. 12A, GMR resistors 194 a-194 d and 196 a-196 d forming the left-most columns of GMR resistor region 44 are respectively interconnected via the associated externally controllable switches to form GMR sensor bridges 204 a and 206 a at a left-most position along x-axis 190 within GMR angle sensor 40. Similarly, as illustrated by FIG. 12B, GMR resistors 194 b, 194 d, 194 e, and 194 f and 196 b, 196 d, 196 e, and 196 f forming the center-most columns of GMR resistor region 44 are respectively interconnected via the associated externally controllable switches to form GMR sensor bridges 204 b and 206 b at a central position along x-axis 190 within GMR angle sensor 40. Also, as illustrated by FIG. 12C, GMR resistors 194 e-194 h and 196 e-196 h forming the right-most columns of GMR resistor region 44 are respectively interconnected via the associated externally controllable switches to form GMR sensor bridges 204 c and 206 c at a right-most position along x-axis 190 within GMR angle sensor 40.

By selecting which GMR resistors 94 a-94 h and 96 a-96 h are connected to form the GRM sensor bridges, the radial position of the GMR sensor bridges of GMR angle sensor 40 relative to ring magnet 32 can be further, and more finely, adjusted to determine a location which provides the least amount of variation in the magnitude of output vector 142.

FIG. 13 is a flow diagram generally illustrating a process 220 for calibrating and operating an off-center angle measurement system according to one embodiment. Process 220 begins at 222 with the mounting of a magnet to a rotating shaft, such as rotating shaft 38, wherein the magnet provides a magnetic field which rotates with the shaft about a rotational axis of the shaft. In one embodiment, the magnet comprises a ring magnet, such as ring magnet 32, mounted about the shaft remote from ends of the shaft.

At 224, an integrated circuit magnetoresistive angle sensor, such as GMR angle sensor 40, is positioned in the magnetic field at a radially off-center position from the axis of rotation. According to one embodiment, the integrated circuit magnetoresistive angle sensor, includes first and second magnetoresistive sensing bridges respectively providing first and second signals representative of orthogonal first and second directional components of the magnetic field. According to one embodiment, the integrated circuit angle sensor includes a set of adjustment parameters for adjusting attributes of the first and second signals. In one embodiment, the set of adjustment parameters includes a first and a second amplitude parameter and a first and a second offset parameter for respectively adjusting an amplitude and an offset of the first and second signals. In one embodiment, the set of adjustment parameters further includes an offset parameter for one of the first and second signals to adjust a phase of the one of the first and second signals. In one embodiment, the first and second magnetoresistive sensing bridges comprises giant magnetoresistive elements. In one embodiment, the first and second magnetoresistive sensing bridges comprises anisotropic magnetoresistive elements.

At 226, a “known” angular position of the shaft is measured, such as by using a discrete-type angle sensor, such as a conventional toothwheel- or polewheel-based angle sensor, for example, which is temporarily coupled to the rotating shaft. At 228, the angular position of the rotating as measured by the integrated circuit magnetoresistive angle sensor, the “measured” angular position, is determined from the first and second signals.

At 230, the values of the set of adjustment parameters are adjusted to modify attributes of the first and second signals to compensate for errors in the measured angular position resulting from structural inaccuracies between the magneto resistive elements of the first and second bridges and from non-uniformity of the magnetic field at the off-center position until an error between the “known” angular position determined at 226 and the “measured” angular position from determined from the integrated circuit at 228 is substantially minimized.

According to one embodiment, process 220 is then complete, as indicated at 232. However, according to one embodiment, as illustrated by the dashed lines at 234, process 220 additionally includes adjusting the radial position of the integrated circuit until variations in a magnitude of a vector based on the first and second signals are substantially minimized.

According to one embodiment, such as described above by FIGS. 11 and 12A-12C, the integrated circuit magnetoresistive angle sensor includes a first set of magnetoresistive elements and an associated first plurality of switches which can be operated to selectively interconnect different subsets of the first set of magnetoresistive elements to form the first magnetoresistive sensing bridge at different positions within the integrated circuit, and a second set of magnetoresistive elements and an associated second plurality of switches which can be operated to selectively interconnect different subsets of the second set of magnetoresistive elements to form the second magnetoresistive sensing bridge at different positions within the integrated circuit.

According to one embodiment, as illustrated by the dashed lines at 236, process 220 includes adjustment of the radial position by operating the first and second pluralities of switches such that the resulting first and second magnetoresistive sensing bridges are at positions within the integrated circuit such that the variations in the magnitude of the vector are substantially minimized.

FIG. 14 illustrates one embodiment of an integrated circuit for measuring an angular position of a magnetic object rotating around an axis. The integrated circuit illustrated in FIG. 14 is configured for measuring the angular position from an off-axis position; this is to say that the integrated circuit according to FIG. 14 does not need to be placed with its sensor elements at a position along the rotation axis. A person of ordinary skill in the art will readily understand that methods and techniques described above may be also implemented using the integrated circuit according to the invention as illustrated in FIG. 14.

The integrated circuit of FIG. 14 illustrates a plurality of switching elements 112-1, 112-2, . . . 112-N; 114-1, 114-2, . . . , 114-N; and 116-1, 116-N in combination with a plurality of sensing elements Sxy, as shall be explained in more detail below.

From a supply rail 100 individual switching elements 112-1, 112-2, . . . 112-N out of the plurality of switching elements provide a switchable connection to individual ones of sensing bridges B1, B2, B3, . . . , BN. Although the supply rail 100 is indicated as a common supply rail 100, there may without any limitation individual supply rails present instead.

The individual sensing bridges B1, B2, B3, . . . , BN are formed by sensing elements Sxy. FIG. 14 depicts four examples of individual sensing bridges with the individual sensing elements Sxy for which the index x runs from 1 to N. Each of the individual sensing bridges B1, B2, B3, . . . , BN comprises four individual sensing elements as indicated by the index y running from 1 to 4. Therefore the first individual sensing bridge B1 is formed by a first individual sensing element S11, a second individual sensing element S12, a third individual sensing element S13 and fourth individual sensing element S14. The other sensing bridges B2, B3, . . . , BN are labelled accordingly.

In the exemplary embodiment of FIG. 14 the individual sensing bridges B1. B2. B3, . . . , BN share a common ground. It is to be understood however that this is an optional choice and by no means limiting to the present invention.

Between the first sensing element Sx1 and the second sensing element Sx2 of each individual sensing bridge B1, B2, . . . , BN a first signal Sig1 may be tapped using a first signal switch 114-1, 114-2, . . . , 114-N, respectively. This is to say the first signal switches 114-1, 114-2, . . . , 114-N provide a switchable connection from each of the individual sensing bridges B1, B2, . . . , BN to a pre-amplifier (not shown) The first signal Sig1 may be representative of a first directional component of the magnetic field sensed by one of the individual sensing bridges B1, B2, B3, . . . , BN due to the rotating object, such as the ring magnet 32, but is not limited thereto. It is to be understood that the first directional component represented by the first signal may however vary from one sensing bridge to another one of the sensing bridges.

It is further conceivable to replace the first signal switches 114-1, 114-2, . . . , 114-N by a non-switchable connection, respectively to the line delivering the first signal Sig1 to a pre-amplifier (not shown). For such a setup it would be of interest to select individual ones of the sensing bridges B1, B2, B3, . . . , BN by switching one of the switches 112-1, 112-2, 112-3, . . . , 112-N ON, while the others are set to an OFF state.

Similar to the first signal switches as explained above, FIG. 14 illustrates second signal switches 115-1, 116-2, 116-3, . . . , 116-N providing a switchable connection from an individual one of the sensing bridges B1, B2, B3, BN to a line forwarding a second signal Sig2 to a further pre-amplifier (not illustrated). It is convenient to tap the second signal Sig2 between the third sensing element Sx3 and the forth sensing element Sx4 of an individual sensing bridge B1, B2, B3, . . . , BN selected by one of the switching elements 112-1, 112-2, 112-3, . . . , 112-N. The second signal Sig2 is typically representative of a second directional component of the magnetic field generated by the rotating object, as was already explained above with regards to the other embodiments. The second directional component may without limitation be perpendicular to the first directional component for which the first signal Sig1 is representative. As explained before, it is to be understood that the second directional component represented by the second signal Sig2 may however vary from one sensing bridge to another one of the sensing bridges. It may be convenient to provide the first signal Sig1 and the second signal Sig2 representing substantially orthogonal directional components of the magnetic field within an individual one of the sensing bridges.

As already explained for the first signal switches alternatively or additionally the second signal switches 116-1, 116-2, 116-3, . . . , 116-N may be replaced by a non-switchable connection from the individual sensing bridge B1, B2, B3, . . . , BN to the line forwarding the second signal Sig2 to the pre-amplifier (not illustrated).

The integrated circuit of FIG. 14 is different than the embodiment pertaining to FIG. 11 with regards to an RDS ON of individual switches within sensing bridges of FIG. 11 may affect a performance of the sensing bridges and consequently affect a sensitivity of the integrated circuit. The integrated circuit disclosed in FIG. 14 however does not contain any switching elements within an individual sensing bridge S1, S2, S3, . . . , SN so that the RDS ON of the individual switches should not affect the performance of the sensing bridges.

A person of ordinary skill will readily appreciate that the individual sensing bridges S1, S2, S3, . . . , SN may be distributed over the integrated circuit in a suitable manner. The interdigital arrangement of sensing bridges S1, S2 and S3 illustrated in FIG. 14 shall therefore be considered as a non-limiting example. As a further example of distributing the sensing bridges, the sensing bridge SN is depicted on the right of FIG. 14, while the sensing bridges S1, S2, and S3 are depicted on the left side of FIG. 14. Distributing the individual sensing bridges S1, S2, S3, . . . , SN may be of interest in order to minimize errors that may be caused by non-uniformity of the magnetic field at the off-axis position. Other spatially varying errors of the sensed magnetic field may be minimized by using a selected one of the sensing bridges S1, S2, S3, . . . , SN. Hence all techniques and methods for minimizing errors explained above may be implemented with regards to the integrated circuit of FIG. 14, too.

FIG. 15 illustrates a further embodiment of an integrated circuit 200. The integrated circuit illustrated in FIG. 15 may be operated in a current mode, which is different than the integrated circuits described before, including the integrated circuit of FIG. 14 operated in voltage mode.

An individual switch 112-1, 112-2, 112-3, 112-N out of a plurality of switches is provided to select an individual sensing element out of a plurality of sensing elements S1, S2, S3, . . . , SN. A voltage controlled current source, for example the operational transductance stage OTA, may be used in combination with a regulating switch 110 for regulated coupling a current Iout1 to the selected one of the individual sensing elements S1, S2, S3, . . . , SN. Other means of (regulated) coupling the current Iout1 to the selected one of the individual sensing elements S1, S2, S3, . . . , SN are conceivable.

A feedback loop for each of the individual sensing elements S1, S2, S3, . . . , SN may be provided in order to regulate a voltage across the selected one of the sensing elements S1, S3, S3, . . . , SN. In the embodiment of FIG. 15 the feedback loop is formed by second switches 111-1, 111-2, 111-3, . . . , 111-N switchably coupling to a feedback path leading to an (inverted) input of the operational transductance stage OTA. With such a setup it is convenient to regulate the voltage across the selected one of the sensing elements S1, S2, S3, . . . , SN. There are various other feedback scenarios conceivable in order to regulate the voltage and/or a current through the selected one of the sensing elements S1. S2, S3, . . . , SN.

The sensing elements S1, S2, S3, . . . , SN share a common ground plate in the setup of FIG. 16, this is however a design choice not relevant to working the present invention.

FIG. 16 illustrates a setup using several of the integrated circuits explained with respect to FIG. 15. It may be of interest to select the sensing elements S1, S2, S3, . . . , SN of the first integrated circuit 200 (for example the top one in FIG. 16) to provide a first signal Iout1. The second integrated circuit of FIG. 16 may instead provide a current Iout2. When performing a subtraction of these signals, as indicated in FIG. 16, one may implement a differential sensing behavior of the integrated circuits 200.

Additionally or alternatively one may arrange the sensing elements S1, S2, S3, . . . , SN of the first integrated circuit 200 (say the top one in FIG. 16) such that the first signal Iout1 corresponds to a first spatial component of the magnetic field caused by the magnetic field of rotating object, as explained above. The sensing elements S1, S2, S3, . . . , SN of the second integrated circuit 200 (the lower one of FIG. 16) may instead provide a signal Iout2 corresponding to a second signal, as explained before, i.e. corresponding to a second spatial component of the magnetic field caused by the magnetic field of the rotating object.

A person of ordinary skill in the art will readily appreciate that the techniques and methods disclosed with regards to the other embodiments may also be implemented using the integrated circuit as illustrated in FIGS. 15 and 16.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof. 

What is claimed is:
 1. A method for off-center measurement of an angular position of a rotating shaft, comprising: providing a magnetic field which rotates with the shaft about an axis of rotation; positioning an integrated circuit having first and second magnetoresistive sensing bridges within the magnetic field at a radially off-center position from the axis of rotation, the first and second magnetoresistive sensing bridges respectively providing first and second periodic signals representative of first and second directional magnetic field components, the integrated circuit having a set of adjustment parameters for modifying attributes of the first and second signals; modifying values of the set of adjustment parameters until errors in the first and second signals are substantially minimized, including errors resulting from the non-uniformity of the magnetic field at the radially off-center position; and determining an angular position of the shaft based on the first and second signals.
 2. The method of claim 1, wherein the set of adjustment parameters includes a first and a second amplitude parameter for respectively adjusting an amplitude of the first and second periodic signals.
 3. The method of claim 1, wherein the set of adjustment parameters includes a first and a second offset parameter for respectively adjusting an offset of the first and second periodic signals.
 4. The method of claim 1, wherein the set of adjustment parameters includes an offset parameter to adjust a phase of one of the first and second periodic signals.
 5. The method of claim 1, including adjusting the radially off-center position until variations in a magnitude of a vector obtained from the first and second periodic signals resulting from the non-uniformity of the magnetic field at the radially off-center position are substantially minimized.
 6. The method of claim 1, where modifying the values of the set of adjustment parameters includes: positioning the shaft at known angular position; and adjusting the values of the set of parameters until an error between an angular position determined from the first and second signals and the known angular position is minimized.
 7. The method of claim 1, wherein providing a magnetic field includes mounting a ring magnet about the rotating shaft away from ends of the shaft.
 8. The method of claim 1, wherein the first and second sensing bridges include magnetic sending elements being one of GMR sensing elements, TMR sensing elements, AMR sensing elements, horizontal Hall sensing elements, and vertical Hall sensing elements.
 9. An integrated circuit for measuring an angular position of a magnetic object rotating about an axis from an off-axis position, the integrated circuit comprising: a first sensing circuit including: a plurality of first magnetic sensing elements, each magnetic sensing element having a first terminal coupled to a same reference potential and having a second terminal; a first voltage controlled current source providing a first current at an output and having a feedback input; a plurality of first switches controllable to couple the second terminal of a selected one of the first magnetic sensing elements to the current source output so that the first current flows through the selected first magnetic sensing element to provide a first sense voltage; and a plurality of second switches controllable to couple the first sense voltage of the selected first magnetic sensing element to the feedback input, the first current being based on the first sense voltage and being representative of a first directional component of a magnetic field formed by the rotating magnetic object.
 10. The integrate circuit of claim 9, wherein the magnetic sensing elements of the first plurality have a resistance which changes based on a strength of the first directional component of the magnetic field.
 11. The integrated circuit of claim 9, wherein each of the first switches is coupled between the second terminal of a different one of the first magnetic sensing elements and the first current source output.
 12. The integrated circuit of claim 9, including a voltage source providing a fixed first reference voltage to a reference voltage input of first current source, the first current source adjust the first current so as to adjust the first sense voltage to match the first reference voltage.
 13. The integrated circuit of claim 9, further including: a second sensing circuit including: a plurality of second magnetic sensing elements, each magnetic sensing element having a first terminal coupled to a same reference potential and having a second terminal; a second voltage controlled current source providing a second current at an output and having a feedback input; a plurality of first switches controllable to couple the second terminal of a selected one of the second magnetic sensing elements to the current source output so that the second current flows through the selected second magnetic sensing element to provide a second sense voltage; and a plurality of second switches controllable to couple the second sense voltage of the selected second magnetic sensing element to the feedback input, the second current being based on the second sense voltage and being representative of a second directional component of a magnetic field formed by the rotating magnetic object.
 14. The integrate circuit of claim 13, wherein the magnetic sensing elements of the second plurality have a resistance which changes based on a strength of the second directional component of the magnetic field.
 15. The integrated circuit of claim 13, wherein each of the first switches is coupled between the second terminal of a different one of the magnetic sensing elements of the second plurality and output of the second current source.
 16. The integrated circuit of claim 13, including a voltage source providing a fixed second reference voltage to a reference voltage input of the second current source, the second current source to adjust the second current so as to adjust the second sense voltage to match the second reference voltage.
 17. The integrated circuit of claim 13, wherein the first directional component is orthogonal to the second directional component.
 18. The integrated circuit of claim 13, the first and second magnetic sensing elements being one of GMR sensing elements, TMR sensing elements, AMR sensing elements, horizontal Hall sensing elements, and vertical Hall sensing elements.
 19. The integrated circuit of claim 9, further including: a second sensing circuit including: a plurality of second magnetic sensing elements, each magnetic sensing element having a first terminal coupled to a same reference potential and having a second terminal; a second voltage controlled current source providing a second current at an output and having a feedback input; a plurality of first switches controllable to couple the second terminal of a selected one of the second magnetic sensing elements to the current source output so that the second current flows through the selected second magnetic sensing element to provide a second sense voltage; and a plurality of second switches controllable to couple the second sense voltage of the selected second magnetic sensing element to the feedback input, the second current being based on the second sense voltage and being representative of the second directional component of the magnetic field formed by the rotating magnetic object.
 20. The integrated circuit of claim 19, further including a subtractor to subtract the second current from the first current to provide differential sensing of the magnetic field component to determine an angular position of the rotating magnetic object. 